The world's higher quality light natural crude oils are those generally having an API gravity greater than 30° with sulfur content less than 0.5 percent. These high quality light natural crudes cost the least to refine into a variety of highest value end products including petrochemicals and therefore command a price premium. More important, however, world refinery capacity is geared to a high proportion of light natural crude oils with an API of 30° or higher.
It is generally accepted that world supplies of light crude oils recoverable by the conventional means of drilling wells into reservoirs and the use of nature's pressure, or by pumping to recover the oil, will be diminished to the extent that in the coming decades these supplies will no longer be capable of meeting the world demand.
To find relief from oil supply shortage it will be necessary to substantially increase processing of the vast world reserves of coal and viscous oil, bitumens in tar sands and kerogens in oil shale. These sources of crude oil remain largely unexploited today although recovery of oil from tar sands is in practice in Canada. The development of technology for the production of synthetic oil as an alternative to the light crude oil found in nature continues to be plagued by the large capital investments required in recovery and production facilities and a long wait for return on investment. In addition, large expenditures are required to construct or retrofit refineries for synthetic oils recovered from heavy oils and bitumens. In addition, present synthetic oil plants for processing heavy oils, or bitumens from tar sands, have focused more on the development of systems for recovery and production than on energy efficiency, maximization of yield and high environmental processing standards. Except for South Africa's Sasol process, which benefits from low cost labor used in coal mining, straight coal liquefaction is not yet cost competitive with synthetic oil produced from tar sands bitumen or heavy oils.
It is therefore of considerable importance that methods are found to produce synthetic crudes to replace the rapidly depleting reserves of light natural crudes available from conventional sources and at a cost at least approaching these crudes and competitive with the crudes being recovered at higher cost from under the sea or from frontier areas such as the extreme north with its rigorous climate. It is also important that synthetic crudes are comprised in desired proportions of a mixture of aromatic, naphthenic and paraffinic components as these three families of compounds comprise essential feedstock to refinery capacity producing today's transportation fuels and feedstocks for the petrochemical industry.
Accordingly, applicants have disclosed an invention which is an innovative hydroconversion processing configuration for converting these heavy oils and/or bitumens to produce a transportable synthetic crude oil. In the invention, the atmospheric residue from the heavy oil or bitumen feedstock is only partially processed in the hydroconversion unit, there is no secondary hydrotreating nor is there any heavy unconverted residue or coke to dispose of using this novel process.
The entire heavy oil or bitumen feedstock is first fractionated in a crude still and thereafter a portion of the straight run atmospheric and/or vacuum residue created in the fractionation process is fed to an ebullated-bed hydroconversion reactor along with a hydrogen stream. The ebullated-bed reactor operates at relatively high severity and gives a conversion rate of greater than seventy (70%) percent. The converted products (975° F.) from the ebullated-bed reactor is thereafter mixed with straight-run distillates, by-passed heavy oil, bitumen atmospheric residue, and unconverted vacuum residue to create the final synthetic crude product.
These and other features of the present invention will be more readily apparent from the following description with reference to the accompanying drawing.